This project will investigate the mechanism of RNA editing which is a newly discovered process that changes the nucleotide sequence of RNA by the addition and/or elimination of uridines. The existence of RNA editing expands our view of how genetic information can be stored and expressed. RNA editing in a sense is the converse of RNA splicing since it creates new nucleotide sequence by net nucleotide addition rather than removal of necleotide sequences. The project is designed to elucidate the mechanism that determines the final nucleotide sequence of the edited RNA. The sequence of events occurring during RNA editing will be studied. Recent experiments suggest that RNA editing is posttranscriptional, does not employ a full template and proceeds in the 3' to 5' direction. The project will investigate where editing is initiated, if it entails RNA cleavage, 5' addition of Us, and relegation of the cleaved fragments and determine the characteristics of these activities. It will examine the possibility that editing employs the activity of other macromolecules or a complex which will be characterize if this is the case.